1. Field of the Invention
The present invention relates to a method and apparatus for cleaning filters, such as air intake filters, ventilation air filters contaminated with dust and other particles, etc.
2. Description of the Related Art
Filters are used in various fields to remove dust and other particles from fluid such as air. For example, medium performance filters are used for air passages in air conditioning systems in buildings or underground shopping malls, and are used in air intake lines of devices such as local gas turbine generators. These filters are used to remove salts, dust, oil particles, fibers and other substances (hereafter collectively referred to as xe2x80x9ccontaminantsxe2x80x9d) from the air by collecting them on a filter media of resin fiber or other materials.
FIGS. 10a and 10b show a perspective view of such filters. The filter F shown in FIG. 10a has a filter media f with a corrugated non woven fabric of resin fibers or of glass fibers, folded in parallel to the corrugation in zigzag pattern and retained within a frame 51. The filter F shown in FIG. 10b has a filter media f folded in zigzag pattern with corrugated separators f(a) inserted between folded filter media and retained within the frame 51.
As an apparatus for cleaning such filters, the applicant has filed a patent application of an ultrasonic cleaning apparatus (Japanese Laid-Open Patent Publication No. Hei 9-276633). In this apparatus, a contaminated filter accommodated on a rack is conveyed by a handling unit to an ultrasonic cleaning tank for cleaning, and a cleaned filter is rinsed in a rinse tank and returned to the rack.
However, filters F cannot always be cleaned under the same condition because the degree of contamination of such filters varies according to their conditions of usage and other factors. For instance, when all filters are cleaned in the condition needed for cleaning heavily contaminated filters, a considerable time loss occurs in the cleaning of less contaminated filters.
On the other hand, when all filters are cleaned in the short period of time needed for cleaning of less contaminated filters, sufficient cleaning effect is not obtained for the heavily contaminated filters, and cleaning of the internal portion of the filter media is sometimes difficult.
Moreover, as filters F has a frame surrounding a complicated filter media, contaminants removed from the filter media tend to reattach on the cleaned filter media, which sometimes makes difficult the complete removal of contaminants.
It is therefore an object of the present invention to provide a method and apparatus for cleaning filters in accordance with the degree of contamination.
In the filter cleaning method according to the present invention, the degree of contamination of the filter media is analyzed to select the cleaning steps of the filter according to the degree of contamination. Heavily contaminated filters are subjected to pretreatment before cleaning, while less contaminated filters are cleaned without pretreatment, and cleaned filters are subjected to a restoration process for preventing decrease in thickness of the filter media after drying. The pretreatment can be performed by a method such as immersing the filter in a pretreatment solution containing a detergent. The restoration can be performed by a method such as immersing the filter media in a restoration solution containing a softener. In this way, the necessity of performing pretreatment is determined according to the degree of contamination, therefore, the heavily contaminated filter media is cleaned effectively by the addition of pretreatment before the cleaning, while the less contaminated filter media is cleaned in a shorter time. Moreover, by utilizing the restoration process after the cleaning, the capturing capacity of contaminants per filtering area is restored to the capacity before the cleaning.
Heavily contaminated filters are preferably subjected to pretreatment and to rinsing of the pretreatment liquid before the cleaning. The contaminants become easily removable by the pretreatment, and a greater part of the contaminants can be removed by the rinsing to significantly enhance the effectiveness of the subsequent cleaning process.
In addition, the sterilization of filters for use in environments which will affect human beings can be performed continuously after the restoration.
Furthermore, by performing processes up to the cleaning and processes after the cleaning in separate systems, the processes up to the cleaning which need longer time, and processes after the cleaning can be performed independently, thus increasing the efficiency and reducing the time needed for performing the cleaning operation.
Ultrasonic cleaning can efficiently remove contaminants within the filter media.
The cleaning unit according to the present invention comprises, means for analyzing the degree of contamination of the filter media, means for arranging the filter in a predetermined location according to the degree of contamination, means for conveying the filter from the predetermined location, means for performing pretreatment when the filter is classified as heavily contaminated, means for cleaning the filter; and means for restoring the filter media for preventing reduction of thickness after the cleaning. With this filter cleaning method and apparatus, the degree of contamination of the filter media is first analyzed by the analysis means and classified according to previously determined standards, and the filter is accommodated at the predetermined location according to the classification. The heavily contaminated filter is conveyed to the pretreatment process, and the less contaminated filter is conveyed directly to the cleaning process by the conveying means. Then the filter media of the cleaned filter is restored. Thus efficient cleaning operation can be performed by selecting the cleaning procedure according to the degree of contamination of the filter media. As a result, by the restoration after the cleaning, sufficient filtering capacity of the cleaned filter can be restored.
In addition, by providing the pretreatment rinsing means, the cleaning effect can be increased because the contaminants have become easily removable by the pretreatment process and can be rinsed away before the cleaning. The pretreatment rinsing means provided by a pretreatment rinse tank having a flow generating means for directing rinsing liquid toward the filter media also enhances the filter cleaning effect.
Filters for use in environments that affect human beings can be sterilized after the cleaning by the sterilization means which is provided after the restoration of the filter media.
Furthermore, by separating conveying means into two separate systems, i.e. conveying means for conveying the filter in processes up to the cleaning of the filter, and conveying means for conveying the filter in processes after the cleaning, cleaning of the filters which need a longer time can be performed simultaneously with other processes such as a restoration process. As result, working efficiency is significantly increased thereby reducing the total work time.
In addition, by forming the cleaning means as an ultrasonic cleaning tank, in which the filter is immersed for a specified amount of time, the contaminants adhered on the filter media can be removed effectively by means of cavitation created by the ultrasonic waves.
Moreover, by conveying means which comprises a filter frame for holding the filter and a conveyor unit which holds the upper portion of the filter frame while conveyed, the conveyor unit can be prevented from being wetted by the cleaning liquid during the pretreatment, cleaning or restoration processes.
These objects as well as other objects, features and advantages of the present invention will become more apparent to those skilled in the art from the following description with reference to the accompanying drawings.